Table of contents

It is shown that the generally accepted so-called re-emission model for the formation of the extended fine Auger structure (EXFAS) in secondary electron spectra above M_2,3VV Auger lines of 3d metals fails to account for this structure. The straight calculations reveal that the 3d indirect excitation (re-emission) process (3p⁶3d¹⁰ to 3p⁵3d¹⁰ epsilon 'd to 3p⁶3d⁹ epsilon f) contributes about 10-15% to the total 3d-shell ionization cross-section in the case of Cu. The mechanism for EXFAS formation is proved to be the same as that for EELFS. Namely, the EXFAS structure is due to the direct electron emission from both 3p and 3d closely spaced shallow levels and is mainly determined by the oscillations of the f-partial density of the final states. The adequacy of the mechanism proposed is confirmed by the reasonable agreement of the theoretical Cu M_2,3 EELFS and EXFAS spectra with the experimental ones.

This letter reports the results of temperature-dependent conductivity measurements performed for a conjugated polymer doped with magnetic complex. There, an abrupt decrease in conductivity was observed as temperature was lowered. The phenomenon is interpreted as the effect of the short-range magnetic order appearing and, consequently, affecting the transport processes by magnetic interactions mediated by charge-carrying species (polarons, bipolarons). In addition, results of X-ray diffraction experiments that were performed are discussed.

The influence of a magnetic field on the thermal conductivity of high-T_c superconductors is described. A semi-phenomenological model which takes into account the influence of the magnetic field on the density of normal electrons as well as on the electron-vortex scattering is used, assuming that the energy levels of quasiparticles near the vortex cores are quantized and supposing that electrons are mainly scattered by these quasiparticles. The experimental results on an untwinned YBa₂Cu₃O_{7- delta} single crystal, on YBa₂Cu₃O_{7- delta} and YBa₂(Cu_0.95Fe_0.05)₃O_{7- delta} ceramics are quite well reproduced with quite realistic values of the physical parameters.

Heterojunctions of undoped solid C₆₀ and n- or p-type-doped crystalline Si have been obtained. Current-voltage measurements show that both C₆₀/n-Si and C₆₀/p-Si contacts are rectifying but their directions of rectification are opposite. Thermal activation measurements at a fixed forward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.30 eV for C₆₀/n-Si and 0.48 eV for C₆₀/p-Si. Using energy-band models for heterojunctions we assign values to the positions of the conduction and valence bands of the solid C₆₀ relative to those of crystalline Si and derive the electron affinity and band gap of solid C₆₀ film as 3.92 eV and <1.72 eV, respectively.

Detailed measurements of the X-ray scattering from a 400 AA thin film of Nb grown on sapphire have been performed using synchrotron radiation from a bending magnet. Bragg reflections from Nb planes perpendicular to the surface normal have a two-component lineshape: a sharp, essentially resolution-limited peak, superimposed on a diffuse Lorentzian-squared component. In contrast, Bragg peaks with a finite wavevector transfer in the plane of the film display the broad component only. These measurements indicate that the lattice mismatch between the metallic overlayer and substrate is relieved by the formation of domains randomly rotated in the plane of the film.

The development of surface contour changes at about the welding interfaces of silver/gold alloy diffusion couples with various terminal gold concentrations has been investigated for an annealing temperature of 1081 K. The surface profiles were measured at nine different annealing times for each of the employed diffusion couples. The cross-sectional areas of the developing bulge and groove increase proportionally with annealing time, as has already been observed in other systems. The results can be described in terms of reduced growth coefficients. The unexpected decrease of the effects at high silver concentrations could be explained by a model of mass compensation based on plastic deformation.

Amorphization was achieved by room-temperature 200 keV xenon ion mixing in Zr-Mo multilayered films. In addition, two new Mo-based metastable crystalline phases were obtained, which were of FCC and HCP structures, respectively. A Gibbs free-energy diagram that concerns the free-energy curves of the amorphous phase and the terminal solid solutions was constructed to give related thermodynamic explanations to the observations.

We study the electronic structure of a Pt overlayer and Pt₇ adatom cluster, respectively, on the Ni(111) surface by using a self-consistent tight-binding model. Together with epitaxial geometries, a mean-field 'non-epitaxial' model is also employed. For these structures, calculations for hydrogen adsorption are performed. Correlation between the geometry, surface reactivity, core-level shifts and local surface electronic structure has been recently discussed for Pd and Pt ultrathin films on BCC substrates. Similar correlation is also found in the present study. Nevertheless, its origin is now traced to the change of the local d-band width due to overlayer compression rather than to a specific hybridization between orbitals on different atoms. An analogy with PtNi alloy surfaces and their catalytic properties is pointed out.

(111) surfaces of copper, grown epitaxially on a clean (001) face of a ruthenium crystal, were exposed to hydrogen or deuterium at pressures p up to 2000 Pa, at temperatures from 290 to 440 K. The concomitant changes of the work function phi were recorded photoelectrically. While coadsorbed impurities influenced the absolute value of phi , the slope d phi /dp was found to be roughly constant and independent of the temperature in the pressure range 400<or=p<or=2000 Pa. The slope of the coverage d theta /dp, calculated from low-temperature adsorption data in the literature, is also constant in the above temperature and pressure range. Thus the variation of phi follows the chemisorption of hydrogen atoms due to the tail of the Boltzmann distribution. The effects of impurity adsorption and desorption are discussed.

We extend and detail a previously developed model for formation of electronic resonances at free-electron-like metal surfaces, in order to calculate scanning tunnelling (ST) spectra. The effect of the tip is mimicked by inclusion of an external field, self-consistently, in a jellium description of the surface potential. The lattice-induced corrugation of the potential is included perturbatively via a pseudopotential. We compare our calculated ST spectra for Al(111) with experimental spectra for that surface and conclude that a peak occurring below the metal vacuum level is a 'crystal-derived' resonance, in the sense that lattice effects are crucial for its manifestation.

We present a full theoretical discussion of the surface polaritons, ATR and oblique incidence reflectivity spectra of layered antiferromagnets. The results apply equally to a large class of easy-plane magnetic systems including artificial magnetic superlattices with antiferromagnetic coupling. It has recently been argued that the conventional calculation of the RF permeability tensor mu is incorrect and should be replaced by a calculation that is consistent with macroscopic electrodynamics. Our computed spectra for NiO lead to the conclusion that the form of mu can be established by comparison with experimental far-infrared spectra.

Reflection spectra for different grazing angles and reflectivity angular dependences of the Si-SiO₂ system with different dioxide thicknesses have been measured in the energy range 40-850 eV, including the Si L_2.3 and O K absorption edges. The angular dependences have been used for the dielectric constant determination. By turning a BN hexagonal crystal and using s-polarized radiation a strong reflectivity dependence on the crystal orientation has been detected. Indicatrices of the surface roughness scattering have been recorded for the BN_hex crystal surface. The statistical properties of the roughness have been investigated by means of perturbation theory. These measurements were obtained using synchrotron radiation, and the interest in the specific properties of this radiation for such measurements is emphasized.

We report the results of positron lifetime and Doppler-broadening measurements in Pd-In beta Hume-Rothery alloys. The combination of these techniques gave new insights into the defect structure of annealed and quenched samples of different compositions. The existence of thermal In vacancies for some compositions has been confirmed.

Vibrational spectra of molecular systems exposed to low-intensity microwave radiation are analysed within an approach that makes the quantum formalism physically integral with the classical one. It is shown that the collective nature of excited vibrational states of molecular aggregates can be the reason for a perceptible transformation of the spectra under microwave radiation even at high temperature.

The electron-phonon interaction causes a spectral thermal shift (TS) in crystals with impurities. In this paper we develop an approach to calculate the different contributions to the TS of MgO:V²⁺ in detail; these include Raman scattering, the direct process and the optical branch. It is found that the direct process plays a predominant role in the TS. Moreover, the TS caused by thermal expansion is interpreted and calculated using the theory of the pressure-induced spectral shift. Taking account of the contributions, we calculated the R-line TS of MgO:V²⁺ by fitting the experimental data. Our results show good agreement with the TS experimental data and other experimental data for MgO:V²⁺.

Phases and phase transitions in the system Ta_1-xNb_xTe₄ are studied for three compositions (x=0, 0.25, 0.5). The various phases are characterized by commensurate and/or incommensurate satellite reflections; the intensity variation of these satellites is analysed and critical exponents are determined: they characterize the type of transition. A tentative phase diagram is proposed.

The relativistic band structure and band-gap bowing factors of ternary II-VI semiconductor alloys containing Cd, Zn, Se and Te are calculated by the ab initio self-consistent pseudopotential method with spin-orbit correction. The disorder in these alloys is modelled by the virtual crystal approximation (VCA). The numerical results thus obtained are compared with experimental data from photoluminescence spectroscopy. The experimental band-gap bowings for this family of alloys are always concave upwards. However, CdSe_xTe_1-x and ZnSe_xTe_1-x in general show much larger bowing factors than Cd_1-xZn_xSe and Cd_1-xZn_xTe. The former two alloys show a minimum in the band gap versus composition curve near x=0.35 while the latter two have it at x=0. Most of these qualitative trends are well explained by VCA. However, in order to explain the large bowing in the first two alloys, some kind of local order has to be incorporated in the calculation. It was found that a local cluster with AuCu-I-like structure, when relaxed, has quite a significant contribution to the bowing factors. The splittings in the band structure due to both spin-orbit and structural relaxation effects are also discussed.

The infinite-U single-impurity Anderson model for rare earth alloys is examined with a new set of self-consistent coupled integral equations, which can be embedded in the large-N expansion scheme (N is the local spin degeneracy). The finite-temperature impurity density of states (DOS) and the spin-fluctuation spectra are calculated exactly up to the order O(1/N²). The presented conserving approximation goes well beyond the 1/N approximation (NCA) and maintains local Fermi-liquid properties down to very low temperatures. The position of the low-lying Abrikosov-Suhl resonance (ASR) in the impurity DOS is in accordance with Friedel's sum rule. For N=2 its shift toward the chemical potential, compared to the NCA, can be traced back to the influence of the vertex corrections. The width and height of the ASR are governed by the universal low-temperature energy scale T_K. Temperature and degeneracy N dependence of the static magnetic susceptibility is found to be in excellent agreement with the Bethe ansatz results. Threshold exponents of the local propagators are discussed. The resonant level regime (N=1) and intermediate-valence regime ( mod epsilon _f mod < Delta ) of the model are thoroughly investigated as a critical test of the quality of the approximation. Some applications to the Anderson lattice model are pointed out.

Local metastable excited states are found in Ar and Kr cryocrystals when He gas-discharge products are trapped in the growing cryocrystals. These states are detected by ESR and are interpreted as being local metastable excited np⁵(n+1)s³P₂ atomic-type states in Ar and Kr cryocrystals. The study showed that the yield of the ³P₂ excitations in the above process decreases with increasing temperature. Analysis of the results allows the following explanation of the observed effect to be given. Metastable excited He atoms from the He gas discharge are trapped in the growing Ar or Kr cryocrystals and transfer their excitation energy to the cryocrystal to form, in the process of internal ionization, a RG⁺ ion and a free electron in the conduction band, whereupon the fast (10^-12 s) self-trapping reaction of a hole follows: RG⁺RG to RG₂⁺. Thereafter either the dissociative recombination reaction RG₂⁺+e to RG₂** to RG+RG*(³P₂) or recombination RG₂⁺+e to RG+RG to produce ground-state atoms could take place. The former is likely at lower temperatures, and the latter at higher temperatures when the vibrational relaxation rate of the RG⁺ molecular ion increases and the mobility of free electrons in the conduction band decreases. This is the reason for the observed temperature dependence.

The static structure factors of the XXZ-model in the presence of a uniform field are determined from an exact computation of the ground states at given total spin on rings with N=4,6,...,28 sites. Against the naive expectation, a weak uniform field strengthens the antiferromagnetic order in the transverse structure factor for the isotropic case.

The magnetic properties of orthorhombic Ho_1-xY_xNi compounds have been studied from resistivity, magnetization and neutron diffraction experiments. The Curie temperatures decrease linearly from 37.5 K in HoNi to 4 K for Ho_0.2Y_0.8Ni, while Ho_0.1Y_0.9Ni and YNi do not present any magnetic long-range order. Below T_C the compounds show a non-collinear magnetic structure belonging to a single irreducible representation, which evolves at lower temperatures towards another non-collinear structure described by the mixture of two irreducible representations. The appearance of both magnetic arrangements is discussed, comparing these structures with those of other rare earth nickel compounds and taking into account both crystalline electric field and exchange interactions.

We made dielectric, magnetic and magnetoelectric measurements on single-crystal samples of TbMn₂O₅, which was an antiferromagnet with the Neel temperature of approximately 40 K. From the results, we concluded that there were two groups of phase transitions at lower temperatures. The first group are three successive transitions at 29.3, 27.2 and 25.6 K, whose natures are probably electric. The crystal is polar below this temperature range, because the polarity of the magnetoelectric effect can be controlled by electric field cooling. Another transition exists at 8 K, where time inversion symmetry breaks. It is related to the ordering of Tb³⁺ magnetic moments.

In the static replica symmetric approximation, a quantum Heisenberg S=1 spin-glass model with single-ion uniaxial anisotropy and infinite-range random Dzyaloshinskii-Moriya (DM) interaction in applied magnetic fields is investigated. The local susceptibility and the corresponding order parameters are calculated numerically, and are found to be in good agreement with those of thermofield dynamics. The dependences of entropy and specific heat on temperature are studied numerically at various magnetic fields. It is shown that the entropy is always positive and the quantum fluctuation has a very strong effect on the specific heat. Especially, the typical crossover behaviour of the specific heat of a spin glass at various magnetic fields for mixed-anisotropy interactions is found.

The dependences of saturation magnetostriction lambda _s and forced-volume magnetostriction delta omega / delta H on the concentration and temperature have been investigated for amorphous La(Fe_xAl_1-x)₁₃ alloys prepared by high-rate DC sputtering. The magnetic phase diagram obtained from the differential magnetic susceptibility dM/dH has been correlated with these magnetostrictions. The spin freezing temperature T_f is drastically decreased but the Curie temperature T_C is slightly increased on application of a magnetic field. The temperature dependences of lambda _s and delta omega / delta H exhibit a broad peak at the spin freezing temperature T_f. The temperature dependence of lambda _s for the ferromagnetic alloys is explained by the two-ion model, reflecting the peculiar amorphous structure consisting of icosahedral clusters. The peak of delta omega / delta H at the Curie temperature becomes indistinct with increasing ferromagnetic state in contrast with the peak at the spin freezing temperature. The giant values of delta omega / delta H and its divergent behaviour at the spin freezing temperature are accounted for by the variable amplitude of the local magnetic moment in the itinerant spin glasses. The significant large delta omega / delta H is connected with the pronounced large magnetovolume and magnetoelastic effects such as the spontaneous volume magnetostriction omega _s, compressibility kappa and high-field susceptibility chi _hf which bring about various Invar anomalies.

Two prominent Fe³⁺ centres were observed by ESR in alpha -TeO₂:Fe single crystals. One of them exhibits C₂ symmetry (Fe³⁺(C₂) centre) and the other one exhibits C₁ symmetry and also superhyperfine interactions with two hydrogens (Fe³⁺-2H-V₀(C₁) centre). The Fe³⁺(C₂) centre is believed to be an interstitial Fe³⁺ ion; the nature of its superhyperfine interaction with neighbouring Te nuclei contributes to this assignment. The Fe³⁺-2H-V₀(C₁) centre is attributed to a substitutional Fe³⁺ ion with two neighbouring hydrogens and a local oxygen vacancy.

This paper reports the photoluminescence (PL) of a silicon oxide film formed by anodization in the electropolishing region in HF solution. The PL is preliminarily believed to be due to certain light-emitting centres in the silicon oxide film. In addition, the paper suggests that not all the PL of anodized silicon formed in HF solution can be solely ascribed to the porous silicon.

The X-ray diffraction radiation from an oscillator (DRO) at a large angle to the particle motion direction is considered. The numerical analysis of the angular and spectral distributions of the X-ray DRO for electrons of medium energies (6-8 MeV) was carried out.

Neutron scattering measurements have been made of the high-energy excitonic excitations of Co²⁺ ions in CoF₂ and CsCoCl₃. The measurements were performed with the HET direct geometry time-of-flight spectrometer on the ISIS pulsed neutron source at the Rutherford Appleton Laboratory. In the case of CoF₂ the results are consistent with previous estimates of the crystal-field and spin-orbit parameters, but for CsCoCl₃ there are marked discrepancies. The results can be fitted by adjusting the crystal-field parameters, but this has the consequence that the exchange interactions between the spins in CsCoCl₃ are anisotropic.

We demonstrate the consistency of the method that introduces two parameters, the inverse of the square root of the spin length and the characteristic soliton length, in the study of solitons in spin systems.

The comment by Shi does not actually offer clear answers to any of the objections that we have made in previous work.